The pesent research program is concerned with 1) a study of the mechanism of activation of prekallikrein, factor XII, and factor XI, and the role of high molecular weight kininogen in these reactions, 2) the isolation and characterization of factor VIII and its role in blood coagulation, 3) the isolation and characterization of the plasma proteins involved in the intrinsic pathway of fibrinolysis, 4) the mechanism of the interaction between the plasma serine proteases involved in blood clotting and the plasma protein inhibitors, such as bovine antithrombin III and the acid-labile antitrypsin inhibitor, 5) the mechanism of inactivation of factor V by activated Protein C, 6) the characterization of Protein S and Protein K of human plasma, 7) the three-dimensional structure of platelet factor 4 and several other plasma proteins, and 8) the biosynthesis of several plasma proteins in cell-free systems.